Camera and adjacent plattforms.

Added more camera movement. If the player is really close to exiting the
screen on top or down side the camera will increase it's speed to follow
faster.

Inside Gridpiece is a field called adjacentPlattforms that will be used
by the rendering later on. If two plattforms are adjacent they will
visually blend into each other.
No more doublejump!

Fixed the double jumping bug and cleaned up a bit of code.
Texture update

Fixed the textures on plattform to differ depending on whether the
adjacent squares are plattforms. Makes it all look really schmexy.
Modes

Added modes to the code. There are currently three modes that modify the
behaviour of the game. Menu, Overworld and Battle. Where the last
haven't been implemented yet.
Menu

Added a menu that is accessible from the game by pressing the 'i'
button. Not much to do inside the menu yet but it will be a fundamental
part of the finished game.
Inventory

Added an early form of inventory.